1. Field of the Invention
The present invention is directed to radical-curable adhesive compositions which include a (meth)acrylate component; a thermal resistance-conferring agent; and a radical cure-inducing composition. Reaction products of the compositions of this invention exhibit superior resistance to thermal degradation.
2. Brief Description of the Technology
Radical-curable adhesive compositions generally are well-known. In the context of anaerobic adhesives, see e.g., R. D. Rich, xe2x80x9cAnaerobic Adhesivesxe2x80x9d in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker. Inc., New York (1994) and references cited therein. In the context of radiation-curable adhesives, see e.g., J.G. Woods, xe2x80x9cRadiation Curable Adhesivesxe2x80x9d in Radiation Curing: Science and Technology, 333-98, S. P. Pappas, ed., Plenum Press, New York (1992).
Uses of radical-curable adhesives are legion and new applications continue to be developed.
In the past, many adhesives particularly anaerobic adhesives, have been rendered resistant to degradation at elevated temperatures by the inclusion of certain additives.
For instance, U.S. Pat. No. 3,988,299 (Malofsky) refers to a heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds.
L. J. Baccei and B. M. Malofsky, xe2x80x9cAnaerobic Adhesives Containing Maleimides Having Improved Thermal Resistancexe2x80x9d in Adhesive Chemicals, 589-601, L-H, Lee, ed., Plenum Publishing Corp. (1984) report the use of maleimidesxe2x80x94specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimidexe2x80x94to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150xc2x0 C.
While the addition to radical-curable adhesive compositions of such maleimide compounds to render them resistant to thermal degradation provides reaction products with acceptable performance, it would be desirable to find alternative compounds to include in such formulations. Moreover, maleimides are known to inhibit photoinitated cure of acrylate-based compositions.
Curing agents for epoxy-containing compounds are known, such as those commercially available from Ajinomoto Co., Tokyo, Japan under the tradename xe2x80x9cAJICURExe2x80x9d, for instance, xe2x80x9cAJICURExe2x80x9d PN-23. See U.S. Pat. No. 4,546,155 (Hirose).
Notwithstanding the state-of-the-technology, there is an on-going search for additives to improve the thermal performance of reaction products of radical-curable adhesives. In addition, it would be desirable from a commercial, economic, environmental, supply and regulatory standpoint to provide alternatives and/or replacements for maleimide-type materials for improving the resistance to thermal degradation of reaction products of radical-curable adhesive compositions.
The present invention meets the desire discussed above by providing radical-curable adhesive compositions, reaction products of which exhibit superior performance at elevated temperatures. The compositions include a (meth)acrylate component; a thermal-resistance conferring agent; and a radical cure-inducing composition.
In another aspect of this invention, radiation-curable compositions are provided, reaction products of which demonstrate superior resistance to thermal degradation.
The invention also provides a process for preparing reaction products from the radical-curable adhesive compositions of the present invention, the steps of which include applying the composition to a desired substrate surface and exposing the coated substrate surface to conditions which are appropriate to effect cure thereofxe2x80x94e.g., exposure to conditions in which air is substantially excluded therefrom for anaerobic application or exposure to radiation in the electromagnetic spectrum for photoinitated applications.
In addition, the invention provides a process for preparing the radical-curable adhesive compositions of the present invention, the steps of which include combining with mixing the (meth)acrylate component, the thermal resistance-conferring agent, and the radical cure-inducing composition.
Also, the invention provides the reaction products so-formed by the above-described process, which reaction products demonstrate superior thermal properties, such as resistance to degradation at elevated temperatures.
The present invention will be more fully appreciated by a reading of the section entitled, xe2x80x9cDetailed Description of the Inventionxe2x80x9d, together with the illustrative examples which follow thereafter and the figures.